E2BE support

package.json

@@ -36,7 +36,7 @@
     "is-my-json-valid": "^2.20.5",
     "js-yaml": "^4.0.0",
     "matrix-appservice": "^0.10.0",
-    "matrix-bot-sdk": "^0.6.0-beta.2",
+    "matrix-bot-sdk": "^0.6.0-beta.4",
     "matrix-js-sdk": "^12.4.1",
     "nedb": "^1.8.0",
     "nopt": "^5.0.0",

src/models/encryption/store.ts

@@ -0,0 +1,40 @@
+import { RustSdkAppserviceCryptoStorageProvider } from "matrix-bot-sdk";
+import { watchFile, promises as fs } from "fs";
+
+/**
+ * The RustSdk Crypto store uses a "sled" DB, which is a flat file KV store
+ * operated on by the rust internals. This class provides a way to synchronise
+ * that dataset in another place (e.g. a PostgreSQL table).
+ */
+export class SynchronisedCryptoStore extends RustSdkAppserviceCryptoStorageProvider {
+
+    private timeout: NodeJS.Timeout|null = null;
+
+    constructor(
+        baseStoragePath: string,
+        onSync: (error: Error|null, data?: Buffer) => Promise<void>,
+        debounceMs = 2500
+    ) {
+        super(baseStoragePath);
+        const sync = () => {
+            fs.readFile(baseStoragePath, null).then((s) => {
+                onSync(null, s);
+            }).catch(onSync);
+            this.timeout = null;
+        };
+
+        watchFile(baseStoragePath, () => {
+            if (this.timeout) {
+                clearTimeout(this.timeout);
+            }
+            this.timeout = setTimeout(() => {
+                sync();
+            }, debounceMs);
+        });
+
+        // Save the file before the process closes.
+        process.on("beforeExit", () => {
+            sync();
+        });
+    }
+}